The art of mixing is highly empirical and to date there has not been developed any formula or equation which can be used to calculate the degree or speed of mixing under a given set of conditions. The fundamental objective to be accomplished by mixing remains essentially the same, namely to achieve uniformity by having each particle of any one material lie as nearly adjacent as possible to a particle of each of the other materials within a given container.
For at least two types of blending operations it would be advantageous to employ a void cap. A void cap can be applied to a container in order to obtain additional space for blending to occur. This is particularly true where containers are shipped essentially full of material leaving little if any space available for blending. Unless a void cap is used it is necessary either to transfer the material to a larger container or to remove a substantial fraction of material before blending can occur. Another instance in which it would be advantageous to employ a void cap is when it is necessary to increase the area of a container for the purpose of adding an additional ingredient or material to material already in the container.
In the past, cones have been attached to ends of containers, such as conventional fiberboard drum containers, 55 gallon drums and other similar types of containers, in order to aid in discharging such containers. One problem associated with the use of cones has been their lack of strength unless made of very heavy material and when they were made of heavy material such as stainless steel their weight and opaqueness were problems. There was also no convenient way to attach the cones to the containers. Moreover, solid particles as well as liquids tended to slide along the cone walls without intermixing. In order to overcome the latter problem, baffles have sometimes been inserted inside the cones. These baffles, however, hinder and sometimes prevent the complete discharge of material from the cone. In addition, the baffles were difficult to clean. These latter factors have tended to limit utilization of cones to the handling of the same type of material in order to avoid contamination problems. Another recognized problem with cones has been the fact that in order to achieve a void space of about 40 percent a given cone must extend a substantial distance from the container making the overall assembly of cone and container unwieldly.